1. Field of the Invention
The present invention relates to displayable characters and more particularly to attributes for characters displayable in a word processing system.
2. Description of the Prior Art
It is desirable in word processing equipment having a display to generate an image on the display which replicates, as nearly as possible, the information which is ultimately printed on a document. In addition to substantive character identifying information, this accurate replication includes attributes of the characters, some of which can be ultimately printed on the document. Typical character attributes include bolded characters, blinking characters, reverse video characters (dark characters on light background), underscored characters and double underscored characters.
Examples of character attributes and their uses are described in co-pending patent application entitled, "Circuit for Controlling Character Attributes in a Word Processing System Having a Display", Ser. No. 177,651, filed Aug. 12, 1980, which issued as U.S. Pat. No. 4,422,070 Dec. 20, 1983.
Two common methods of providing attribute information have heretofore been used in conventional word processing systems. The first method requires the use of character spaces on the display to represent an attribute. This method is not desirable in word processing applications where importance is placed on displaying characters and their locations with respect to each other as they would appear when printed or typed. The use of character spaces to represent attributes, therefore, is unacceptable both due to the positioning of characters relative to each other and due to the resulting detrimental effect on the margins of the lines in which these spaces occur.
The second common method of providing attribute information requires no character spaces but uses so-called invisible attributes, provided as a function of a cathode ray tube (CRT) controller, such as a Model No. 8275 CRT controller available from the Intel Corp. This device has provision for only 16 attributes, however, which is insufficient for defining one or more attributes per character for up to 80 characters on each line of displayed text.
Another problem encountered in word processing systems can be related to the aforementioned methods of handling character attribute information. This is the problem of providing one or more sets of characters in addition to a standard set of characters. It is often desirable to be able to print or display characters used in languages such as Greek, Russian, French or Japanese, in addition to English. Similarly certain characters are often required for scientific or mathematical documents. Moreover, type styles such as elite, pica, gothic, italics and modern may be used frequently in certain situations.
Word processing systems generally cannot accommodate the visual display of such stylistic demands, or can accommodate them only approxmately and with a considerable amount of effort. For example, a common technique of obtaining a printout of extraordinary characters such as those mentioned above requires an operator to replace the conventional character set print wheel of a so-called daisy wheel printer with a special character set print wheel before instructing the system to print the extraordinary characters. In many cases, however, the display of the document to be printed does not accurately represent the extraordinary characters. While on these systems a document may be successfully printed using different character type fonts, and the number of character sets may be limited only by the number of character print wheels available, a corresponding display exhibits only one type font, so the extraordinary characters to be printed are not accurately represented on the display.
One of the earliest systems that incorporated two type fonts in a printer control system is disclosed in U.S. Pat. No. 3,283,305 issued to Hans, et al. In that system, two font formats are distinguished: human readable and machine readable fonts, such as MICR or OCR symbols. Codes are presented representing a particular font in which the respective information is to be printed and subsequently the information in either of the two fonts is stored in the same typeline buffer positions as the other font. The appropriate synchronization signal causes the information to be typed in the selected font. A typeline comprises 120 print wheels, one for each column of print, and each having 58 characters, human and machine readable, spaced about the periphery thereof. While the system disclosed in Hans, et al. may be adequate for printing either of two type fonts, no system is therein disclosed for accurately representing each of the type fonts on a visual display.